The invention relates to a fixing element provided with an expander member and having retaining means arranged at its rear end for clamping an article.
German patent document DE-OS 29 14 739 discloses a fixing element which in the region of its leading end face has an expansion zone which is formed by a longitudinal slot having a base which slopes up towards the leading end and an expander member inserted in the longitudinal slot. Anchoring of such fixing element is effected such that, after driving the shank into a hole pre-drilled in a building component, as the article to be fixed is being clamped to the building component the shank is displaced axially with respect to the expander member which digs into wall of the drilled hole. By virtue of the fact hat the base of the longitudinal slot receiving the expander member slopes upwards, the expander member is pressed radially outward and the fixing element is consequently wedged in the drilled hole. The disadvantage of the known fixing element, however, is that the expander member has teeth on its external surface which form straight edges projecting beyond the shank transversely to the longitudinal direction. These edges taking up the entire width of the expander member present a high resistance as the fixing element is being driven into the building component. In particular in the case of a building component consisting of concrete, in addition to the high resistance to driving which is not conducive to easy assembly, this resistance can result in damage to the fixing element which impairs the anchoring function. Moreover, the expander member scrapes material from the inner wall of the drilled hole during the driving-in operation. That material collects in the longitudinal slot and may possibly lead to the expander member's becoming hammed in the longitudinal slot. This causes the displaceability of the expander member in the longitudinal slot to be impaired to such an extent that subsequent expansion after the anchoring operation, in the event that the drilled hole widens as a result of cracks forming, is not possible. Because of this drawback, the known fixing element is not suitable for use in the tensile zone, in which cracks occur. A further reason why it is unsuitable for the tensile zone and why it has relatively low holding values, even in uncracked concrete, is attributable in the known fixing element to the bounding of the longitudinal slot towards the leading end of the fixing element by a stop face. As a consequence, on the one hand only a slight ascending angle for the base of the longitudinal slot can be achieved on the other hand the length of the expander member must also be considerably shortened relative to the length of the longitudinal slot in order to obtain a satisfactory displacement travel for the anchoring. If in addition further widening of the drilled hole occurs as a result of cracks forming, there is a risk that the expander member will bear against the leading stop face of the longitudinal groove and not offer any further expansion potential. This situation can also occur, for example, when the hole to be pre-drilled for the fixing element turns out to be somewhat larger than expected as the hole is being prepared.
Finally, the planar base of the longitudinal slot and planar bearing surface of the expander member provide a high contact pressure during the expansion process which can lead to cold welding. As a result, subsequent expansion and consequently suitability for use in the tensile zone are also impaired.
German patent document DE 33 34 754 C2 discloses an expansible plug, the plug body of which is of sleeve-shaped construction having an internal thread for a screw or threaded rod. The wedge-shaped expander member of this expansible plug is a part of the plug body and is joined to the plug body by way of a web remaining between incisions and acting as a desired rupture point. The incisions are arranged so that on the one hand an inclined face Sloping up towards the leading end of the plug body, and on the other hand the wedge shape of the expander element, are formed. In order to provide a surface for the application of an expansion tool, a stop member projecting into the sleeve bore of the plug body is integrally formed on the expander element.
In order to anchor the expansible plug, the expander member is first torn off at the desired rupture point using an expansion tool and then displaced towards the leading end of the plug body. The tearing off alone of the desired rupture point demands a pushing force that requires the known expansible plug to be braced at the bottom of the drilled hole. Moreover, to bridge the incisions separating the two sliding surfaces of the plug body and the expander element, a relatively large axial displacement of the expander element is required, in order to achieve an expansion effect. Since, furthermore, both the expander element and the plug body consist of the same material, there is a risk that during the expansion the two sliding surfaces will be damaged by cold welding and binding such that no subsequent expansion occurs. The known expansible plug is therefore unsuitable for use in the tensile zone in which drilled holes may widen as a result of cracks forming, requiring compensation through subsequent expansion.